Previous research indicates that the amplitude of the overt (whole body) startle reaction is, in part, determined by the acoustical and visual events that precede presentation of the startle eliciting stimulus. Proposed research will examine the effects of various antecedent visual and acoustic stimuli on the startle reaction of rats and/or pigeons as well as the effects of various antecedent acoustic and visual signals on the human eyeblink elicited by a tap to the glabella (the flat patch of skin between the eyebrows). In general the work with humans will focus on attentional effects in the reflex modification afforded by an appropriate prior signal. More specifically it will determine the manner in which the reflex inhibiting effects of the prior signal are changed by procedures designed to control the subjects focus of attention at the moment that the prior signal occurs.